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they would probably prevail at the expense of those which
did not proceed as quickly. If there is no evidence of
this, there is evidently no variety of structure on which
Natural Selection can act.
But it might be said that what is not true in the case of
fission is true in connection with the phenomenon of con
jugation. Mr. Spencer argues that,—
“along with that remai'kable process which, beginning in minute forms
with what is called conjugation, developed into sexual generation,
there came into play causes of frequent and marked fortuitous
variations. The mixtures of constitutional proclivities, made more or
less unlike by unlikenesses of physical conditions, inevitably led to
occasional concurrences of forces producing deviations of structure.
These were, of course, mostly suppressed, but sometimes increased
by survival of the fittest.”—(p. yj.)
In reply to this argument, we must ask once more what
we really mean by “ fortuitous ” variations. All scientific
people, I suppose, would denounce the idea that these
variations arise by chance, accepting that word in the
ordinary unphilosophical sense of the word. If we say
that these variations arise from causes of which we are
ignorant, that cannot help any physical or biological
theory. The scientific man may be compelled to tolerate
such ignorance as exists for the present, but he denies
that there is any point beyond which research cannot be
successful. He believes that there is a physical cause for
every phenomenon which can be proved to exist. By him
every problem is regarded as capable of solution, if still
unsolved. We may apply this principle to two kinds
of variation : the modifications due to all the conceiv
able influences which act on organisms, directly or
indirectly; and the variations which are the inevitable
result of sexual reproduction, the results of which cannot
be foreseen by man, but the causes of which would per
haps be clear if we could see the process which takes